The subject matter of the present invention is zirconic acid esters which are stable and soluble in water without decomposition.
Organic derivatives of zirconic acid Zr(OH).sub.4 are very useful, reactive chemicals. Particularly important representatives of this group are tetraalkyl zirconates, such as for example tetrapropylzirconate and zirconic acid chelates, the most frequently used chelating agents being acetylacetone and triethanolamine. When these chelating agents are used, however, chelates are obtained which are very poorly soluble in any of the common solvents, or they lead to alkalinely reacting compounds.
These known zirconic acid esters and chelates are used as catalysts for polymerization, polyaddition and esterification and transesterification reactions, as crosslinking agents for polymeric substances such as organopolysiloxanes, nitrocellulose or resins containing hydroxyl groups, in the preparation of coatings, precision casting molds, textile finishing agents or water-repellentizing agents, and as an active agent for the surface treatment of glass. In any case, they are used in a water-free medium or water-free solvents, although the use of water is often desirable for economic and ecological reasons. The versatility of the zirconates as catalysts and crosslinking agents is based on the great reactivity of these compounds. At the same time, this reactivity always interferes with the use of these compounds when water is present in the reaction mixture. Alkyl zirconates even react with atmospheric moisture, so that dilutions with 96% pure alcohol already result in precipitation to zirconium hydroxide.
Attempts have therefore been made to stabilize these known zirconium compounds against the action of water. For example, it is proposed in German Federal Patent No. 22 04 531 to add to solutions of zirconium propylate or butylate such chelating agents as acetylacetone or acetic acid ester, hydroxycarboxylic acids, or polyvalent alcohols, leaving the alcohol that is split off, in addition to the 20 to 30% of the solvent alcohol originally present in the zirconate. The products thus obtained, however, are not pure compounds, but mixtures of the starting products with zirconium acetylacetonates or zirconium chelates of the other chelating agents in an alcoholic solution. If, for example, a mixture obtained in this manner with acetylacetone is concentrated by evaporation, a poorly soluble zirconium acetylacetonate then precipitates as a solid from this solution.
In a second method described in German Federal Patent No. 11 22 049, water-soluble metal alcoholates are obtained by reacting metal alcoholates of lower alcohols with special alcohols of longer chain length. These alcohols are obtained by adding ethylene oxide onto organic compounds having at least 4 carbon atoms and one active hydrogen atom. In the case of zirconium, compounds are thus formed which do hydrolyze after several hours of immersion in water, but their zirconium oxide content is greatly reduced; in the example of the zirconium tetraethylate mentioned therein it drops from 45.4% to 12.6%.
The problem therefore existed of finding zirconium esters of high zirconium oxide content which are liquid, which are soluble in water without the precipitation of insoluble hydrolyzates, and whose aqueous solutions have a neutral reaction.